More flexibility for voxel types outside the volume

[David Williams]

Currently the outside of a volume is considered to be empty space. One of the side-effects of this is that a mesh is also generated in the underside of a terrain volume, which may be undesirable if the player is never actually able to view the terrain from underneath.

Therefore it might be useful to allow the 'outside voxel type' to be specified, and for this to be set separately for each face of the volume (possibly via flags). But also consider what would happen if a voxel is both below and to the left of the volume, and the flags for these two directions are different.

Actually this might all become irrelevant once volumes are considered infinite, and the rendered terrain is just a view onto part of the volume?